API Testing: 30 Interview Questions and Answers

Overview

This guide presents 30 technical interview questions and structured answers focusing on API testing fundamentals through advanced concepts. Topics include distinctions between REST and SOAP, HTTP method idempotency, status code verification, request structure, JSON schema validation, and business logic assertions. It also details boundary value analysis, negative testing strategies, and the separation of authentication from authorization using JWTs and access controls. Advanced sections address API chaining, test isolation, pagination, filtering, and contract compatibility. The text provides guidance on mock usage, asynchronous API testing, rate limiting, and safe retries with idempotency keys. Additionally, it outlines automation framework architecture, CI pipeline integration, failure debugging steps, and a complete order API interview scenario.

Table of contents

1. API Testing Foundations
2. HTTP Methods & Status Codes
3. Requests, Schema & Assertions
4. Positive, Negative & Boundary Tests
5. Authentication & Authorization
6. Test Data & API Chaining
7. Lists & API Compatibility
8. Mocks, Contracts & Async APIs
9. Performance, Limits & Retries
10. Automation, CI & Debugging
11. Interview Scenario: Order API

Selected preview

API testing checks a service through its interface, without relying on the UI. Tests should verify inputs, outputs, business rules, permissions, and side effects.

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